In-Situ Thermal Response Fluid Characterization

ABSTRACT

Tools, processes, and systems for in-situ fluid characterization based on a thermal response of a fluid are provided. The thermal response of a downhole fluid may be measured using a downhole thermal response tool and compared with thermal responses associated with known fluids. The properties of the downhole fluid, such as heat capacity, diffusivity, and thermal conductivity, may be determined by matching the thermal response of the downhole fluid with a thermal response of a known fluid and using the properties associated with the known fluid. The composition of the downhole fluid may be determined by matching the viscosity of the downhole fluid to the viscosity of known fluid. A downhole thermal response tool for cased wellbores or wellbore sections and a downhole thermal response tool for openhole wellbores or wellbore sections are provided.

BACKGROUND Field of the Disclosure

The present disclosure generally relates to analysis of fluids inhydrocarbon reservoirs. More specifically, embodiments of the disclosurerelate to a downhole tool for the in-situ characterization of fluids inhydrocarbon reservoirs.

Description of the Related Art

Wells may be drilled into rocks to access fluids stored in geographicformations having hydrocarbons. Such a geographic formation may containor be referred to as a “reservoir.” Information about fluids in ahydrocarbon reservoir is important for properly characterizing thereservoir and conducting optimal drilling and production operations toefficiently extract hydrocarbons. Increasing the accuracy of thisinformation may increase the accuracy of subsequent determinations usedto characterize a reservoir. Various devices and techniques exist fordetermining the fluids information, such as downhole tools and coresampling of reservoir rock. These techniques have particular limitationsand costs and may not provide the most accurate fluids information. Forexample, many devices and techniques are incapable of direct in-situdetermination of fluids information. Moreover, the determination andinaccuracy of some fluids information may result in delays in drillingand production.

SUMMARY

Embodiments of the disclosure generally relate to the in-situcharacterization of downhole fluids, such as oil, water, and oil-watermixtures, via a thermal response (for example, a cooling rate, heatingrate, or both).

In one embodiment, a tool for determining the thermal response of adownhole fluid is provided. The tool includes a tool body defining afluid inlet and an interior chamber configured to receive a fluid and aplurality of temperature sensors disposed at a respective plurality ofpositions along an axial length of the tool body. Each of the pluralityof temperature sensors is configured to acquire a temperaturemeasurement of the fluid and a heating element disposed at a positionalong the axial length of the tool body such that the heating element isdisposed between two of the plurality of temperature sensors and theheating element is configured to heat the fluid. In some embodiments,the heating element is a ceramic mesh heating element coupled to aradiofrequency (RF) antenna. In some embodiments, each of the pluralityof temperature sensors is a thermocouple. In some embodiments, each ofthe plurality of temperature sensors is an infrared sensor. In someembodiments, the heating element is a first heating element, theposition is a first position, and the tool includes a second heatingelement disposed at a second position along the axial length of the toolbody such that the heating element is disposed between a different twoof the plurality of temperature sensors. The second heating element isconfigured to heat the fluid. In such embodiments, the first heatingelement is configured to heat to a first temperature and the secondheating element is configured to heat to a second temperature.

In another embodiment, a tool for determining the thermal response of adownhole fluid. The tool includes a tool body and a plurality oftemperature sensors disposed at a respective plurality of positionsalong an axial length of the tool body. Each of the plurality oftemperature sensors configured to acquire a temperature measurement of afluid external to the tool body. The tool further includes a heatingelement disposed at a position along the axial length of the tool bodysuch that the heating element is disposed between two of the pluralityof temperature sensors, the heating element configured to heat a regionexternal to the tool body. In some embodiments, the heating element is aradiofrequency (RF) source coupled to a directional RF antenna. In someembodiments, the RF source is a rotational RF source rotatable around acircumference of the tool body. In some embodiments, each of theplurality of temperature sensors is a thermocouple. In some embodiments,each of the plurality of temperature sensors is an infrared sensor. Insome embodiments, the heating element is a first heating element, theposition is a first position, the region comprises a first region, andthe tool includes a second heating element disposed at a second positionalong the axial length of the tool body such that the heating element isdisposed between a different two of the plurality of temperaturesensors. The second heating element is configured to heat the fluid. Insuch embodiments, the first heating element is configured to heat to afirst temperature and the second heating element is configured to heatto a second region external to the tool body.

In another embodiment, a method of determining the properties of a fluidis provided that includes inserting a tool into a wellbore. The toolincludes a tool body and a plurality of temperature sensors disposed ata respective plurality of positions along an axial length of the toolbody. Each of the plurality of temperature sensors is configured toacquire a temperature measurement of the fluid. The method furtherincludes receiving a respective plurality of temperature measurementsfrom the plurality of temperature sensors of the tool, determining athermal response of the fluid based on the plurality of temperaturemeasurements, and determining at least one property of the fluid usingthe thermal response. In some embodiments, determining a property of thefluid using the thermal response includes matching the thermal responseof the fluid to a thermal response of a known fluid and determining aproperty of the fluid from a property of the known fluid. In someembodiments, the at least one property includes at least one of a heatcapacity, a diffusivity, and a thermal conductivity. In someembodiments, determining the thermal response of the fluid based on theplurality of temperature measurements includes plotting the plurality oftemperature measurements versus time. In some embodiments, each of theplurality of temperature sensors is a thermocouple. In some embodiments,the tool body defines a fluid inlet and an interior chamber configuredto receive the fluid. In such embodiments, the tool includes a heatingelement disposed at a position along the axial length of the tool bodysuch that the heating element is disposed between two of the pluralityof temperature sensors and is configured to heat the fluid. In suchembodiments, the heating element is a first heating element, theposition is a first position, and the tool includes a second heatingelement disposed at a second position along the axial length of the toolbody such that the heating element is disposed between a different twoof the plurality of temperature sensors. In such embodiments, the secondheating element is configured to heat the fluid. In some embodiments,the tool includes a heating element disposed at a position along theaxial length of the tool body such that the heating element is disposedbetween two of the plurality of temperature sensors. In suchembodiments, the heating element configured to heat a region external tothe tool body. In such embodiments, the heating element includes a firstheating element, the position is a first position, the region comprisesa first region, and the tool includes a second heating element disposedat a second position along the axial length of the tool body such thatthe heating element is disposed between a different two of the pluralityof temperature sensors. In such embodiments, the second heating elementis configured to heat the fluid. In some embodiments, the at least oneproperty comprises viscosity and the method includes determining acomposition of the fluid using the viscosity and at least onetemperature of the plurality of temperature measurements. In someembodiments, determining a composition of the fluid using the viscosityand at least one temperature of the plurality of temperaturemeasurements includes matching the viscosity of the fluid at the atleast one temperature to the viscosity of a known fluid and determininga composition of the fluid from the composition of the known fluid.

In another embodiment, a system for determining the properties of afluid in a wellbore is provided. The system includes a processor and anon-transitory computer-readable memory accessible by the processor andhaving executable code stored thereon. The executable code includes aset of instructions that causes the processor to perform operationsinclude receiving a respective plurality of temperature measurementsfrom the plurality of temperature sensors of a tool inserted in thewellbore, determining a thermal response of the fluid based on theplurality of temperature measurements, and determining at least oneproperty of the fluid using the thermal response. In some embodiments,determining a property of the fluid using the thermal response includesmatching the thermal response of the fluid to a thermal response of aknown fluid; and determining a property of the fluid from a property ofthe known fluid. In some embodiments, the at least one property includesat least one of a heat capacity, a diffusivity, and a thermalconductivity. In some embodiments, determining the thermal response ofthe fluid based on the plurality of temperature measurements includesplotting the plurality of temperature measurements versus time. In someembodiments, the at least one property is viscosity and the operationsinclude determining a composition of the fluid using the viscosity andat least one temperature of the plurality of temperature measurements.In some embodiments, determining a composition of the fluid using theviscosity and at least one temperature of the plurality of temperaturemeasurements includes matching the viscosity of the fluid at the atleast one temperature to the viscosity of a known fluid and determininga composition of the fluid from the composition of the known fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a graph of an example thermal response of an oil-watermixture of 10% oil and 90% water in accordance with an embodiment of thedisclosure;

FIG. 2 is a schematic diagram of a downhole thermal response tool fordetermining the in-situ thermal response of a fluid in accordance withan embodiment the disclosure;

FIG. 3 is a flowchart of a process for determining the fluid propertiesof a downhole fluid using a downhole thermal response tool in accordancewith an embodiment the disclosure;

FIG. 4 is a schematic diagram of a downhole thermal response tool fordetermining the in-situ thermal response of a fluid in an openhole wellin accordance with an embodiment the disclosure;

FIG. 5 is a flowchart of a process for determining the fluid propertiesof a downhole fluid using a downhole thermal response tool in accordancewith an embodiment the disclosure;

FIG. 6 depicts a graph of viscosity vs. temperature behavior for engineoil, water, and a water-oil mixture in accordance with an embodiment ofthe disclosure;

FIG. 7 is a flowchart of a process for determining the composition of adownhole fluid using a downhole thermal response tool in accordance withan embodiment the disclosure; and

FIG. 8 is a schematic diagram of a well site having a downhole thermalresponse tool and a thermal response processing system in accordancewith an embodiment of the disclosure.

DETAILED DESCRIPTION

The present disclosure will be described more fully with reference tothe accompanying drawings, which illustrate embodiments of thedisclosure. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to the illustratedembodiments. Rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art.

Downhole fluids, such as oil, water, and oil-water mixtures, may exhibita thermal response (for example, a heating rate) when exposed to heatsource, and may exhibit a thermal response (for example, a cooling rate)in the absence of the heat source. The thermal response may be afunction of various thermal properties of the fluids, such as heatcapacity, diffusivity, and thermal conductivity. The heating rate andcooling rate for a known fluid may be obtained from a database of fluidinformation or from analysis in a lab. For example, an oil-water mixtureof 10% oil and 90% water exhibits a specific thermal response that maybe shown as a thermal response curve. FIG. 1 depicts a graph 100 of anexample thermal response of an oil-water mixture of 10% oil and 90%water in accordance with an embodiment of the disclosure. As shown inFIG. 1, the y-axis 102 depicts the temperature (in ° C.) and the x-axis104 depicts the time (in seconds). The line 106 depicts the increase intemperature by heating the oil-water mixture with a heating source from10 seconds to 80 seconds and recording the temperature every 10 seconds.The line 108 depicts the decrease in temperature from 80 seconds to 10seconds after removing the heating source and recording the temperatureevery 10 seconds. As shown in FIG. 1, the oil-water mixture may exhibitspecific thermal responses, such as when the fluid is heated as shown byline 106 and when the fluid is cooled as shown by line 108, that may beused to match unknown fluids having a similar thermal response.

With the foregoing in mind, embodiments of the disclosure are directedto tools, processes, and systems for in-situ fluid characterizationbased on a thermal response of a fluid. As discussed in the disclosure,the thermal response of a downhole fluid may be measured using adownhole thermal response tool. The thermal response may be comparedwith thermal responses associated with known fluids. The properties of afluid, such as heat capacity, diffusivity, and thermal conductivity, maybe determined by matching the thermal response of the downhole fluidwith a thermal response of a known fluid and using the propertiesassociated with the known fluid.

In some embodiments, the viscosity of a fluid may be determined from thethermal response of the fluid. The composition of the fluid may then bedetermined using the viscosity and temperature measurements by matchingthe viscosity at a temperature to the viscosity of a known fluid havinga known composition.

In some embodiments, a downhole thermal response tool for casedwellbores or cased wellbore sections may include a tool body thatdefines a fluid inlet and an interior chamber for receiving a fluid. Thedownhole thermal response tool may include temperature sensors disposedalong an axial length of the tool body and one or more heating elementsdisposed at positions along the axial length of the tool body, such thata heating element is disposed between two temperature sensors. Theheating elements may heat a fluid in the interior chamber of thedownhole thermal response tool, and the temperature sensors may acquiretemperature measurements of the fluid as it is heated and subsequentlycools. The temperature measurements may be used to determine the thermalresponse of the downhole fluid. The thermal response may be compared tothe thermal responses of known fluids to identify properties of thefluid, as discussed in the disclosure.

In some embodiments, a downhole thermal response tool for openholewellbores or openhole wellbore sections may include a tool body havingtemperature sensors disposed along an axial length of the tool body andone or more heating elements disposed at positions along the axiallength of the tool body that are configured to heat a surroundingformation. The heating elements may heat a fluid in the formationsurrounding the downhole thermal response tool, and the temperaturesensors may acquire temperature measurements of the surrounding fluid asit is heated and subsequently cools. The temperature measurements may beused to determine the thermal response of the downhole fluid, and thethermal response may be compared to the thermal responses of knownfluids to identify properties of the fluid.

FIG. 2 is a schematic diagram of a downhole thermal response tool 200for determining the in-situ thermal response of a fluid andcorresponding fluid properties in accordance with an embodiment thedisclosure. The downhole thermal response tool 200 includes a tool body202 defining an interior chamber 204 and a fluid inlet 206. The downholethermal response tool 200 may include one or more temperature sensors208 and one or more heating elements 210. Each of the heating elements210 may be coupled to a radiofrequency (RF) antenna 212.

The temperature sensors 208 may be positioned to measure the temperatureof a fluid flowing through the interior chamber 204 of the tool 200. Insome embodiments, each of the temperature sensors 208 may be athermocouple or an infrared (IR) sensor. In some embodiments, thetemperature sensors 208 may be a combination of thermocouples and IRsensors. In other embodiments, the temperature sensors may include othersuitable types of temperature sensors. As will be appreciated, each ofthe temperature sensors 208 may be fiber optic and may, in someembodiments, be a circular sensor disposed around an inner circumferenceof the tool body 202.

The heating elements 210 may be positioned to heat the temperature of afluid flowing through the interior chamber 204 of the tool 200. In someembodiments, each heating element 210 may heat to a differenttemperature. For example, in such embodiments, the heating element 210Amay heat to a first temperature and the heating element 210B may heat tosecond temperature. The heating elements 210 may each be a filament orother heating element. In some embodiments, the heating elements 210 mayeach be a ceramic mesh heating element activated by radiofrequency (RF)antennas 212. In some embodiments, for example, such a ceramic meshheating element may be activated by one of the correspondingradiofrequency (RF) antennas 212 before using the tool 200 to determinethe thermal response of a fluid. The ceramic mesh heating elements maybe activated before using the tool to provide a heating time periodsufficient for the ceramic mesh heating elements to reach a specifictemperature. By way of example, some embodiments of a ceramic meshheating element may reach a specific temperature in a heating timeperiod of about 3 minutes.

The temperature sensors 208 and heating elements 210 may work incombination to determine the thermal response of a fluid flowing throughthe interior chamber 202 of the tool 200. An example operation of thetemperature sensors 208 and heating elements 210 is described infra.However, it should be appreciated that other embodiments of the tool 200may include different numbers of temperature sensors and heatingelements that operate in a manner similar to that described in thedisclosure.

In the embodiment shown in FIG. 2, a fluid may enter the interiorchamber 204 via the fluid inlet 202, as shown by arrow 214. An initialtemperature of the fluid may be measured by temperature sensor 208A. Thefluid may subsequently be heated by heating element 210A activated by RFantenna 212A, and the increased temperature of the heated fluid may bemeasured by temperature sensor 208B. In the embodiment shown in FIG. 2,the fluid may be subsequently heated by ceramic heating element 210Bactivated by RF antenna 212B, and the increased temperature of theheated fluid may be measured by temperature sensor 208C. Next, theadditional temperature sensors 208 located downstream of the temperaturesensor 208C may measure decreased in temperature of the fluid as thefluid cools while flowing through the interior chamber 204. For example,temperature sensors 208 D and 208E may measure the temperature of thefluid as it flows through the interior chamber 204 to exit the tool viaa fluid outlet 216. In this manner, a temperature profile of the fluidflowing through the tool 200 may be determined.

In other embodiments, a tool may have more or less heating elements andtemperature sensors. For example, although the tool 200 shown in FIG. 2includes two pairs of a heating element and downstream temperaturesensor, other embodiments of the tool may include three pairs of aheating element and downstream temperature sensor, four pairs of aheating element and downstream temperature sensor, five pairs of aheating element and downstream temperature sensor, or greater than fivepairs of a heating element and downstream temperature sensor. In someembodiments, the tool may include more than one temperature sensordownstream of the ceramic heating element and upstream of the nextceramic heating element. In some embodiments, the tool 200 may includemore than two temperature sensors after a heating element and downstreamtemperature sensor pair and before the fluid outlet of the tool 200.

FIG. 3 depicts a process of operation of the tool 200 in accordance withan embodiment of the disclosure. Initially, the tool 200 may be insertedin a wellbore and positioned at an appropriate distance within thewellbore suitable for measuring a fluid of interest (block 302). Next,the heating elements of the tool 200 may be activated to heat to adesired temperature (block 304). After the heating elements have reacheda desired temperature, the temperature measurements of the fluid flowingthrough the tool 200 may be acquired using the temperature sensors(block 306). In some embodiments, the temperature measurements may beacquired over a duration. In some embodiments, a single set oftemperature measurements may be acquired over the duration. For example,the initial temperature measurement may be acquired at time (t)=0, andthe additional temperature measurements may be acquired at t+n, whereinn is an amount of time. For example, if n=2 seconds, the initialtemperature measurement may be acquired at t=0, the temperaturemeasurement from the second temperature sensor may be acquired at 2seconds, the temperature measurement from the third temperature sensormay be acquired at 3 seconds, the temperature measurement from thefourth temperature sensor may be acquired at 4 seconds, and so on. Insome embodiments, multiple sets (for example, multiple temperaturemeasurements from each temperature sensor or multiple temperaturemeasurements from one or more temperature sensors) may be acquired overthe duration.

After acquiring the temperature measurements of the fluid flowingthrough the tool 200, the thermal response of the fluid may bedetermined (block 308). In some embodiments, for example, thetemperature measurements may be transmitted to the surface over aconnection, and the thermal response may be determined at the surface bya thermal response determination system. After determination of thethermal response, the thermal response of the downhole fluid may becompared to a database of thermal responses, and a match may bedetermined. As will be appreciated, the match may be determined usingknown techniques for curve matching. After matching the thermal responseof the downhole fluid to a thermal response of a known fluid, the fluidproperties of the downhole may be determined from the thermal propertiesof the known fluid (block 310).

FIG. 4 is a schematic diagram of a downhole thermal response tool 400for determining the in-situ thermal response of a fluid andcorresponding fluid properties in an openhole well in accordance with anembodiment the disclosure. The downhole thermal response tool 400includes a tool body 402, one or more temperature sensors 404 and one ormore heating elements (for example, RF sources 406). Each of the RFsources 406 may be coupled to a radiofrequency (RF) antenna 408. Incontrast to the tool 200 shown in FIG. 2 and described supra, thedownhole thermal response tool 400 does not include an interior chamberthat receives a fluid for flowing through the tool. As described infra,the downhole thermal response tool 400 directs heat into a surroundingformation to heat a surrounding fluid and then measure the temperatureof the fluid.

The temperature sensors 404 may be positioned to measure the temperatureof a fluid surrounding. In some embodiments, each of the temperaturesensors 404 may be a thermocouple or an infrared (IR) sensor. In someembodiments, the temperature sensors 404 may be a combination ofthermocouples and IR sensors. In other embodiments, the temperaturesensors may include other suitable types of temperature sensors. As willbe appreciated, each of the temperature sensors 404 may be fiber opticand may, in some embodiments, be a circular sensor disposed around anouter circumference of the tool body 402.

As shown in FIG. 4, the RF sources 406 and associated RF antennas 408may be positioned to direct heat to a respective target zones and heat afluid surrounding the tool body 402. In some embodiments, the RF sources406 may each positioned internally within the tool body 402. The RFsources 406 may be activated to generate energy directed to the targetzones 410 via the directional antennas 408. The directional antennas 408may any suitable directional antenna that provides a specific voluminouscoverage of the target zones 410. In some embodiments, the directionalantennas 408 may each be a circumferential antenna that is disposedaround a 360° circumference of the tool body 402 at a specific locationalong the length of the tool body 402.

In some embodiments, for example, the RF sources 406 may be activated toprovide a heating time period sufficient for the target zones 410 toreach a specific temperatures. In some embodiments, each RF source 406may heat to a different temperature. For example, in such embodiments,the RF source 406A may heat to a first temperature and the RF source406B may heat to second temperature.

In some embodiments, the RF sources 406 may each be a rotatable RFsource that is rotatable around the circumference of the tool body 402.In such embodiments, each rotatable RF source may be an electrically orhydraulically rotatable RF source such as known in the art. For example,in some embodiments, each RF source 406 may be coupled to an electricmotor that rotates an associated RF source in response to a controlsignal transmitted to the tool 400. As shown in FIG. 4 for example, theRF source 406A may be rotated to correspondingly rotate the target zone410A around the circumference of the tool body 402. In such embodiments,an RF source may be used to heat a target zone and temperaturemeasurements may be acquired after a fluid in the target zone is heated.After heating, the RF source may be rotated around the circumference(for example, 360°) of the tool body 402, additional temperaturemeasurements may be acquired as the previously heated fluid in thetarget zone cools. In some embodiments, the speed of the rotation of theRF source may be controlled to control (for example, increase ordecrease) the time for the RF source to rotate around the circumferenceof the tool body 402. In this manner, multiple temperature measurementsof a heated and cooled fluid in a target zone may be obtained.

The temperature sensors 404, the RF sources 406 and associated RFantennas 408 may work in combination to determine the thermal responseof a fluid surrounding the tool body 402 of the tool 400. An exampleoperation of the temperature sensors 404, the RF sources 406 andassociated RF antennas 408 is described infra. However, it should beappreciated that other embodiments of the tool 400 may include differentnumbers of temperature sensors and heating elements that operate in amanner similar to that described in the disclosure.

After positioning the tool 400 in an openhole wellbore, an initialtemperature of a surrounding fluid may be measured by temperature sensor404A. The surrounding fluid in the target zone 410A may be heated by RFsource 406A and directional antenna 408A. The increased temperature ofthe heated fluid may be measured by temperature sensor 404B. In theembodiment shown in FIG. 4, a second initial temperature of asurrounding fluid may be measured by temperature sensor 404C. Thesurrounding fluid in the target zone 410B may be heated by RF source406B and directional antenna 408B. The increased temperature of theheated fluid may be measured by temperature sensor 406D. In this manner,a temperature profile of fluid surrounding the tool 402 may bedetermined.

In other embodiments, the tool 400 may have more RF heating componentsand temperature sensors. For example, although the tool 400 shown inFIG. 2 includes two sets of a RF heating components and temperaturesensor, other embodiments of the tool may include three sets of a RFheating components and temperature sensor, four sets of a RF heatingcomponents and temperature sensor, five sets of a RF heating componentsand temperature sensor, or greater than five sets of a RF heatingcomponents and temperature sensor.

FIG. 5 depicts a process of operation of the tool 400 in accordance withan embodiment of the disclosure. Initially, the tool 400 may be insertedin an openhole wellbore and positioned at an appropriate distance withinthe wellbore suitable for measuring a fluid of interest (block 502). Insome embodiments, the tool 400 may include a number of heating elementsand temperature sensors sufficient to measure a single zone in theopenhole wellbore, multiple zones in the openhole wellbore, or theentire wellbore.

Next, the heating elements of the tool 400 may be activated to heat to adesired temperature and subsequently heat the surrounding formation andfluid (block 504). After the heating elements have reached a desiredtemperature, the temperature measurements of the fluid surrounding thetool 400 may be acquired using the temperature sensors (block 506). Insome embodiments, the temperature measurements may be acquired over aduration. In some embodiments, a single set of temperature measurementsmay be acquired over the duration. For example, the initial temperaturemeasurement may be acquired at time (t)=0, and the additionaltemperature measurements may be acquired at t+n, wherein n is an amountof time. For example, if n=2 seconds, the initial temperaturemeasurement may be acquired at t=0, the temperature measurement from thesecond temperature sensor may be acquired at 2 seconds, the temperaturemeasurement from the third temperature sensor may be acquired at 3seconds, the temperature measurement from the fourth temperature sensormay be acquired at 4 seconds, and so on. In some embodiments, multiplesets (for example, multiple temperature measurements from eachtemperature sensor or multiple temperature measurements from one or moretemperature sensors) may be acquired over the duration.

After acquiring the temperature measurements of the fluid surroundingthe tool 400, the thermal response of the fluid may be determined (block508). In some embodiments, for example, the temperature measurements maybe transmitted to the surface over a connection, and the thermalresponse may be determined at the surface by a thermal responsedetermination system. After determination of the thermal response, thethermal response of the downhole fluid may be compared to a database ofthermal responses, and a match may be determined. As will beappreciated, the match may be determined using known techniques forcurve matching. After matching the thermal response of the downholefluid to a thermal response of a known fluid, the fluid properties ofthe downhole may be determined from the thermal properties of the knownfluid (block 510).

In additional embodiments, a downhole thermal response tool may be usedto determine the viscosity and, from the viscosity the composition, of adownhole fluid. FIG. 6 depicts a graph 600 of the viscosity vs.temperature behavior for engine oil, water, and a water-oil mixture inaccordance with an embodiment of the disclosure. As shown in FIG. 6, they-axis 102 depicts the viscosity (in centistokes (cSt)) and the x-axis604 depicts the temperature (in ° C.). As shown in FIG. 6, line 106depicts the viscosity vs. temperature behavior for an engine oil, line108 depicts the viscosity vs. temperature behavior for an engine oil,and line 110 depicts the viscosity vs. temperature behavior for water.For each temperature, each composition shown in the graph 600 has aviscosity determined along the respective viscosity vs. temperatureline. For example, at a temperature of 60° C., the line 110 indicatesthat water has a viscosity of about 0.1 cSt, and the line 106 indicatesthat the water-oil mixture has a viscosity of about 0.5 cSt.

Accordingly, in some embodiments the thermal response of downhole fluidobtained using the downhole thermal response tool described in thedisclosure may be used to determine the viscosity of the downhole fluid.Using the viscosity, the composition of the downhole fluid may bedetermined. FIG. 7 depicts a process 700 for determining the compositionof a downhole fluid using a downhole thermal response tool in accordancewith an embodiment of the disclosure. Initially, the tool 700 may beinserted in a wellbore (for example, a cased wellbore or an openholewellbore using the appreciate embodiment of the downhole thermalresponse tool) and positioned at an appropriate distance within thewellbore suitable for measuring a downhole fluid of interest (block702).

Next, the heating elements of the tool may be activated to heat to adesired temperature (block 704). After the heating elements have reacheda desired temperature, the temperature measurements of the downholefluid (for example, the fluid in the tool body in a cased wellbore orsurrounding the tool body in an open hole wellbore) may be acquiredusing the temperature sensors (block 708). In some embodiments, thetemperature measurements may be acquired over a duration. In someembodiments, a single set of temperature measurements may be acquiredover the duration. For example, the initial temperature measurement maybe acquired at time (t)=0, and the additional temperature measurementsmay be acquired at t+n, wherein n is an amount of time. For example, ifn=2 seconds, the initial temperature measurement may be acquired at t=0,the temperature measurement from the second temperature sensor may beacquired at 2 seconds, the temperature measurement from the thirdtemperature sensor may be acquired at 3 seconds, the temperaturemeasurement from the fourth temperature sensor may be acquired at 4seconds, and so on. In some embodiments, multiple sets (for example,multiple temperature measurements from each temperature sensor ormultiple temperature measurements from one or more temperature sensors)may be acquired over the duration.

After acquiring the temperature measurements, the thermal response ofthe fluid may be determined (block 708). In some embodiments, forexample, the temperature measurements may be transmitted to the surfaceover a connection, and the thermal response may be determined at thesurface by a thermal response determination system. After determinationof the thermal response, the viscosity of the downhole fluid may bedetermined using known correlations between the time and temperature ofthe thermal response and viscosity (block 710). In some embodiments,correlations may be determined in via laboratory analysis of fluids bymeasuring the viscosity when measuring the thermal responses of fluids.For example, viscosity may be determined from a heating time at atemperature and a cooling time at a temperature. The viscosity at atemperature within the measured thermal response may then be used todetermine the composition of the downhole fluid by comparison toviscosities of known fluids at the same temperature (block 712). Forexample, as shown in FIG. 6, a viscosity at a particular temperature(for example, the temperature of a heating element in the downholethermal response tool) may be indicative of the composition of a fluid.The viscosity at a particular temperature may be matched to a viscosityof a known fluid at the same temperature. For example, the viscosity ofthe downhole fluid may be compared to a database of viscosities, and amatch may be determined. In this manner, a downhole fluid may beidentified as oil, water, an oil-water mixture of a particular ratio,etc.

FIG. 8 depicts a well site 800 that includes a downhole thermal responsetool 802 for determining a thermal response of a downhole fluid and athermal response processing system 804 in accordance with an embodimentof the disclosure. In the illustrated embodiment, the downhole thermalresponse tool 802 is inserted in well 804 defining a wellbore 806extending into a formation 810. The wellbore 806 may be, for example,the wellbore 806 of any suitable type of well, such as exploration well,a crestal well, or other types of wells drilled to explore a reservoir.

As will be appreciated, FIG. 8 depicts a well site 800 that may includea cased wellbore or an openhole well. That is, the wellbore 806 shown inFIG. 8 may represent a cased wellbore or an openhole wellbore.Accordingly, the downhole thermal response tool 802 may includeembodiments such as the downhole thermal response tool 200 describedsupra and suitable for use in a cased wellbore or the downhole thermalresponse tool 400 described supra and suitable for use in an openholewellbore.

The wellbore 806 may include any form of a hole formed in a geologicformation, such as for the purpose of locating and extractinghydrocarbons or other resources from the formation 810. For example, theformation 810 may include an oil and gas reservoir, and the wellbore 806may include a wellbore drilled into the formation 810 for the purpose oflocating and obtaining information about the oil, gas and otherhydrocarbons in the reservoir.

In some embodiments, the downhole thermal response tool 802 may be awireline tool suspended on a wireline 812. The wireline 812 may includea conductor and may enable data transmission between the wireline tool802 and a wireline monitoring and control system 814. For example,control signals may be transmitted to the wireline tool 802 to controloperation of the tool 802, such as initiating the heating of a heatingelement, stopping the heating of a heating element, rotating a heatingelement, acquiring temperature measurements from temperature sensors,and so on. The wireline 812 may be raised and lowered within the well804 to various depths using devices known in the art, such as a reel anddrum apparatus in a service truck having the various components of awireline system. The monitoring and control system 814 may facilitateoperation of the wireline tool 802 in the wellbore 806 and may receivedata from tool 802 to produce temperature data 816 (for example,temperature measurements). The monitoring and control system 814 mayinclude one or more computer systems or devices. The monitoring andcontrol system 812 may store the temperature data 816 and, in someembodiments, may have the capability of analyzing the temperature data816 in accordance with techniques described in the disclosure. In someembodiments, as shown in FIG. 8, the temperature data 816 may becommunicated to another system (for example, the thermal responseprocessing system 804) for analysis.

Although the embodiment shown in FIG. 8 depicts a wireline tool, inother embodiments, the downhole thermal response tool 802 may be adaptedfor use as other suitable tools for insertion in to the wellbore 806. Inother embodiments, the downhole thermal response tool 802 may bedeployed in other manners, such as by a slickline, coiled tubing, or apipe string. For example, in some embodiments, the downhole thermalresponse tool 802 or its functionality can be incorporated into ameasurement-while-drilling (MWD) apparatus or logging-while-drilling LWDapparatus (such as in a bottomhole assembly). An MWD or LWD apparatusmay have components or functionality in common with wireline tools (forexample, transmitting and receiving antennas, sensors, etc.), but may bedesigned and constructed to endure and operate during drilling.

As described in the disclosure, embodiments of the thermal response tool802 may temperature sensors and heating elements to enable themeasurement of temperatures of downhole fluids and the subsequentdetermination of the thermal response (for example, the heating andcooling rates) of the fluids. As described in the disclosure, thetemperature measurements may be used by the thermal response processingsystem 804 to determine a reference bulk volume of oil, a calculatedbulk volume of oil, and a free water level, as described in thedisclosure.

In some embodiments, the thermal response processing system 804 may beused to determine the fluid properties of a downhole fluid based on athermal response determined from temperature measurements acquired bythe downhole thermal response tool 802. The fluid properties may then beused to further plan and perform exploration, management, and assessmentof the reservoir.

FIG. 8 also depicts components of the thermal response processing systemin accordance with an embodiment of the disclosure. As shown in FIG. 8,the thermal response processing system may include a processor 820, amemory 822, and a display 824. It should be appreciated that the thermalresponse processing system may include other components that are omittedfor clarity, such as a network interface, input device, etc.

The processor 820 (as used the disclosure, the term “processor”encompasses microprocessors) may include one or more processors havingthe capability to receive and process well log data, such as datagenerating from a wireline tool or from a logging while drilling tool.In some embodiments, the processor 820 may include anapplication-specific integrated circuit (AISC). In some embodiments, theprocessor 820 may include a reduced instruction set (RISC) processor.Additionally, the processor 820 may include a single-core processors andmulticore processors and may include graphics processors. Multipleprocessors may be employed to provide for parallel or sequentialexecution of one or more of the techniques described in the disclosure.The processor 820 may receive instructions and data from a memory (forexample, memory 822).

The memory 822 (which may include one or more tangible non-transitorycomputer readable storage mediums) may include volatile memory, such asrandom access memory (RAM), and non-volatile memory, such as ROM, flashmemory, a hard drive, any other suitable optical, magnetic, orsolid-state storage medium, or a combination thereof. The memory 822 maybe accessible by the processor 820. The memory 822 may store executablecomputer code. The executable computer code may include computer programinstructions for implementing one or more techniques described in thedisclosure. For example, the executable computer code may includethermal response determination instructions 826 to implement one or moreembodiments of the present disclosure. In some embodiments, the thermalresponse determination instructions 826 may receive, as input,temperature data 816 and provide, as output, a thermal response of adownhole fluid associated with the temperature data 816. The outputs maybe stored in the memory 822.

Additionally, the memory 822 the executable computer code may includefluid properties determination instructions 828 and a fluids database630 to implement one or more embodiments of the present disclosure. Thefluid properties determination instructions 828 may receive, as input, athermal response of a downhole fluid determined by the thermal responsedetermination instructions 828. As described in disclosure, the thermalresponse of the downhole fluid may be compared to thermal responses ofknown fluids. For example, the fluids databases 630 may include knownfluids and associated thermal responses and fluid properties. Asdescribed supra, by comparing the thermal response of the downhole fluidto the thermal responses of known fluids from the database 828, fluidproperties of the downhole fluid may be determined.

The display 824 may include a cathode ray tube (CRT) display, liquidcrystal display (LCD), an organic light emitting diode (OLED) display,or other suitable display. The display 824 may display a user interface(for example, a graphical user interface). In accordance with someembodiments, the display 824 may be a touch screen and may include or beprovided with touch sensitive elements through which a user may interactwith the user interface. In some embodiments, the display 824 maydisplay the thermal response, fluid properties, or both of a downholefluid measured by the downhole thermal response tool 802 in accordancewith the techniques described in the disclosure.

In some embodiments, the thermal response processing system 804 mayinclude a network interface (not shown) that may provide forcommunication between the thermal response processing system and otherdevices. The network interface may include a wired network interface.The network interface may communicate with networks, such as theInternet, an intranet, a wide area network (WAN), a local area network(LAN), a metropolitan area network (MAN) or other networks.Communication over networks may use suitable standards, protocols, andtechnologies, such as Ethernet Bluetooth, Wireless Fidelity (Wi-Fi)(e.g., IEEE 802.11 standards), and other standards, protocols, andtechnologies.

In some embodiments, the thermal response processing system 804 may becoupled to an input device (for example, one or more input devices). Theinput devices may include, for example, a keyboard, a mouse, amicrophone, or other input devices. In some embodiments, the inputdevice may enable interaction with a user interface displayed on thedisplay 824. For example, in some embodiments, the input devices mayenable the entry of inputs to a process for determining free water leveland parameters used in the process (for example, parameters of aselected water saturation model used in the determination of thecalculated bulk volume of oil discussed in the disclosure).

The downhole thermal response tool and associated fluid propertiesdetermination described supra improve the accuracy of the determinationof downhole fluids and provides a more direct measurement of such fluidproperties. The more accurate fluid properties may improve the drillingof wells to access hydrocarbon reservoirs in formations and may increasehydrocarbon production from a hydrocarbon reservoir. Moreover, thedownhole thermal response tool may also provide for faster and lesscostly determinations of downhole fluid properties as compared toexisting techniques that may require fluid sampling and fluid separationprior to analysis. Moreover, the fluid properties determinationdescribed supra may be more computationally efficient than previoustechniques, For example, as compared to previous techniques, the fluidproperties determination may reduce the computation cost and timerequired to determine the fluid properties of downhole fluids in aformation having a hydrocarbon reservoir.

Ranges may be expressed in the disclosure as from about one particularvalue, to about another particular value, or both. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value, to the other particular value, or both, along withall combinations within said range.

Further modifications and alternative embodiments of various aspects ofthe disclosure will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the embodiments described inthe disclosure. It is to be understood that the forms shown anddescribed in the disclosure are to be taken as examples of embodiments.Elements and materials may be substituted for those illustrated anddescribed in the disclosure, parts and processes may be reversed oromitted, and certain features may be utilized independently, all aswould be apparent to one skilled in the art after having the benefit ofthis description. Changes may be made in the elements described in thedisclosure without departing from the spirit and scope of the disclosureas described in the following claims. Headings used described in thedisclosure are for organizational purposes only and are not meant to beused to limit the scope of the description.

What is claimed is:
 1. A tool for determining the thermal response of adownhole fluid, comprising: a tool body defining a fluid inlet and aninterior chamber configured to receive a fluid; a plurality oftemperature sensors disposed at a respective plurality of positionsalong an axial length of the tool body, each of the plurality oftemperature sensors configured to acquire a temperature measurement ofthe fluid; and a heating element disposed at a position along the axiallength of the tool body such that the heating element is disposedbetween two of the plurality of temperature sensors, the heating elementconfigured to heat the fluid.
 2. The tool of claim 1, wherein theheating element comprises a ceramic mesh heating element coupled to aradiofrequency (RF) antenna.
 3. The tool of claim 1, wherein each of theplurality of temperature sensors comprises a thermocouple.
 4. The toolof claim 1, wherein each of the plurality of temperature sensorscomprises an infrared sensor.
 5. The tool of claim 1, wherein theheating element comprises a first heating element and the positioncomprises a first position, the tool comprising a second heating elementdisposed at a second position along the axial length of the tool bodysuch that the heating element is disposed between a different two of theplurality of temperature sensors, the second heating element configuredto heat the fluid.
 6. The tool of claim 5, wherein the first heatingelement is configured to heat to a first temperature and the secondheating element is configured to heat to a second temperature.
 7. A toolfor determining the thermal response of a downhole fluid, comprising: atool body; a plurality of temperature sensors disposed at a respectiveplurality of positions along an axial length of the tool body, each ofthe plurality of temperature sensors configured to acquire a temperaturemeasurement of a fluid external to the tool body; and a heating elementdisposed at a position along the axial length of the tool body such thatthe heating element is disposed between two of the plurality oftemperature sensors, the heating element configured to heat a regionexternal to the tool body.
 8. The tool of claim 7, wherein the heatingelement comprises a radiofrequency (RF) source coupled to a directionalRF antenna.
 9. The tool of claim 8, wherein the RF source comprises arotational RF source rotatable around a circumference of the tool body.10. The tool of claim 7, wherein each of the plurality of temperaturesensors comprises a thermocouple.
 11. The tool of claim 7, wherein eachof the plurality of temperature sensors comprises an infrared sensor.12. The tool of claim 7, wherein the heating element comprises a firstheating element, the position comprises a first position, and the regioncomprises a first region, the tool comprising a second heating elementdisposed at a second position along the axial length of the tool bodysuch that the heating element is disposed between a different two of theplurality of temperature sensors, the second heating element configuredto heat the fluid.
 13. The tool of claim 12, wherein the first heatingelement is configured to heat to a first temperature and the secondheating element is configured to heat to a second region external to thetool body.
 14. A method of determining the properties of a fluid,comprising: inserting a tool into a wellbore, the tool comprising: atool body; and a plurality of temperature sensors disposed at arespective plurality of positions along an axial length of the toolbody, each of the plurality of temperature sensors configured to acquirea temperature measurement of the fluid; receiving a respective pluralityof temperature measurements from the plurality of temperature sensors ofthe tool; determining a thermal response of the fluid based on theplurality of temperature measurements; and determining at least oneproperty of the fluid using the thermal response.
 15. The method ofclaim 14, wherein determining a property of the fluid using the thermalresponse comprises: matching the thermal response of the fluid to athermal response of a known fluid; and determining a property of thefluid from a property of the known fluid.
 16. The method of claim 14,wherein the at least one property includes at least one of a heatcapacity, a diffusivity, and a thermal conductivity.
 17. The method ofclaim 14, wherein determining the thermal response of the fluid based onthe plurality of temperature measurements comprises plotting theplurality of temperature measurements versus time.
 18. The method ofclaim 14, wherein each of the plurality of temperature sensors comprisesa thermocouple.
 19. The method of claim 14, wherein the tool bodydefines a fluid inlet and an interior chamber configured to receive thefluid, the tool comprising: a heating element disposed at a positionalong the axial length of the tool body such that the heating element isdisposed between two of the plurality of temperature sensors, theheating element configured to heat the fluid.
 20. The method of claim19, wherein the heating element comprises a first heating element andthe position comprises a first position, the tool comprising a secondheating element disposed at a second position along the axial length ofthe tool body such that the heating element is disposed between adifferent two of the plurality of temperature sensors, the secondheating element configured to heat the fluid.
 21. The method of claim14, wherein the tool comprises: a heating element disposed at a positionalong the axial length of the tool body such that the heating element isdisposed between two of the plurality of temperature sensors, theheating element configured to heat a region external to the tool body.22. The method of claim 21, wherein the heating element comprises afirst heating element, the position comprises a first position, and theregion comprises a first region, the tool comprising a second heatingelement disposed at a second position along the axial length of the toolbody such that the heating element is disposed between a different twoof the plurality of temperature sensors, the second heating elementconfigured to heat the fluid.
 23. The method of claim 14, wherein the atleast one property comprises viscosity, wherein the method comprisesdetermining a composition of the fluid using the viscosity and at leastone temperature of the plurality of temperature measurements.
 24. Themethod of claim 23, wherein determining a composition of the fluid usingthe viscosity and at least one temperature of the plurality oftemperature measurements comprises matching the viscosity of the fluidat the at least one temperature to the viscosity of a known fluid; anddetermining a composition of the fluid from the composition of the knownfluid.
 25. A system for determining the properties of a fluid in awellbore, the system comprising: a processor; a non-transitorycomputer-readable memory accessible by the processor, the memory havingexecutable code stored thereon, the executable code comprising a set ofinstructions that causes the processor to perform operations includereceiving a respective plurality of temperature measurements from theplurality of temperature sensors of a tool inserted in the wellbore;determining a thermal response of the fluid based on the plurality oftemperature measurements; and determining at least one property of thefluid using the thermal response.
 26. The system of claim 25, whereindetermining a property of the fluid using the thermal responsecomprises: matching the thermal response of the fluid to a thermalresponse of a known fluid; and determining a property of the fluid froma property of the known fluid.
 27. The system of claim 25, wherein theat least one property includes at least one of a heat capacity, adiffusivity, and a thermal conductivity.
 28. The system of claim 25,wherein determining the thermal response of the fluid based on theplurality of temperature measurements comprises plotting the pluralityof temperature measurements versus time.
 29. The system of claim 25,wherein the at least one property comprises viscosity, the operationscomprising determining a composition of the fluid using the viscosityand at least one temperature of the plurality of temperaturemeasurements.
 30. The system of claim 29, wherein determining acomposition of the fluid using the viscosity and at least onetemperature of the plurality of temperature measurements comprisesmatching the viscosity of the fluid at the at least one temperature tothe viscosity of a known fluid; and determining a composition of thefluid from the composition of the known fluid.